1. Field of the Invention
The present invention is directed to an improved process for preparing triarylboranes by reacting an alkali metal, an organohalide, and an orthoborate ester and for the recovery of the borane.
2. Description of the Prior Art
Organoboranes, i.e. compounds having one or more carbons bonded to boron, have been prepared by a variety of methods including the Grignard reaction using reagents of RMgX type in ether solutions of boron halides. U.S. Pat. No. 2,880,242 discloses an improved process for preparing trisubstituted boranes by the direct action of an organic halide and boron halide in dry ethereal solutions with an alkali metal.
U.S. Pat. No. 3,119,857 discloses the preparation of organoboron compounds by reacting an organo-alkali metal with a boron trihalide or an ester of boric acid in an inert liquid reaction medium to produce the corresponding organoboron halide or organo boric acid ester.
Another process for the preparation of organoboron compounds is disclosed in U.s. Pat. No. 3,187,054 which method involves reacting a boron trihalide, boron ester or boron-carbon compound with an organosodium compound in an inert hydrocarbon solvent. The preparation of a variety of aryl polyboronic acids and esters by reacting an aromatic halide with finely dispersed metallic sodium in the presence of a borate ester preferably at atmospheric pressure and at temperatures below about 50.degree. C. is disclosed in U.S. Pat. No. 3,090,801. The preparation of the sodium hydroxide salt of triphenylborane by reacting triphenylborane with sodium hydroxide is disclosed by Wittig and Raff in an article entitled Uber Komplexbildung mit Triphenyl-bor, Ann. 573, 208 (1951). The preparation of related compounds, e.g. alkyl phosphines, is disclosed in U.S. Pat. No. 3,223,736.